A PON (Passive Optical Network) is one of configurations for implementing FTTH (Fiber To The Home) that provides each home with network access service through an optical fiber. A feature of the PON lies in that optical access service can be provided at low cost by making communication with a part of the optical fiber, which connects between a home-side device (an optical network unit (ONU)) and a subscriber line terminal (an optical line terminal (OLT)), being commonly used.
In a network system including the FTTH, a new function is frequently required to be added and a function to solve a problem is frequently required. A method for implementing such functions is to download a software program to be executed by a CPU (Central Processing Unit) in a network device, or to download design data of an FPGA (Field Programmable Gate Array) in the network device. It should be noted that a term “firmware” herein includes a program code to be executed by a CPU provided in a communication device (irrespective of the OLT and the ONU), as well as a configuration code of the FPGA.
For example, Patent Document 1 (Japanese Patent Laying-Open No. 2010-252176) discloses a communication system configured such that an OLT broadcasts, to a plurality of ONUs, data that should be downloaded by the plurality of ONUs. The data that should be downloaded by the plurality of ONUs can include firmware for updating firmware embedded in each of the plurality of ONUs. According to the above-described configuration, the download by the plurality of ONUs connected to the PON can be done in a short time.